Fuel cells provide increased efficiency and energy density relative to internal combustion engines and secondary batteries. By converting chemical energy directly into electrical energy, less thermal waste is created than in a heat engine, see Bockris, J. O. 'M; Srinivasan, S. Fuel Cells: Their Electrochemistry; McGraw Hill: New York, 1969. While hydrogen fuel cells are efficient and may become a major source of energy in the next millennium, they are not practical for all purposes. The infrastructure for distribution of hydrogen is not well developed, as it is for liquid and gaseous hydrocarbon fuels, and the latter present clear advantages for transportation, home power generation, and remote power applications.
Reforming of fossil fuels can provide a route for their use in hydrogen-air fuel cells: 
The hydrogen evolved from the reforming process can be used in well known air breathing polymer electrolyte membrane (PEM) fuel cells which perform the following half-cell reactions:2H2(g)→+4H(aq)++4e−E°=OV vs. NHE  (2)O2(g)+4H(aq)++4e−→2H2O(1)E°=+1.23 V vs. NHE  (3)
The anode catalysts used in reformate gas fuel cells are simple alloys and metals such as platinum and platinum-ruthenium alloy. After steam reforming and subsequent fuel processing steps, low-temperature water gas shift and partial oxidation of the fuel, a small amount of carbon monoxide, 10-100 ppm, is still present. The anode catalyst is quickly poisoned by the carbon monoxide and thereby rendered inoperable. Therefore, with current catalysts, the reformate gas requires an additional purification step such as pressure-swing adsorption to remove the carbon monoxide. However, the purification process and equipment greatly adds to the weight and expense of the overall fuel cell system. Another solution is to find effective catalysts that rapidly oxidize or that are not poisoned by carbon monoxide.
There is presently no reliable theory for predicting the catalytic behavior of ternary and higher alloys, or even for predicting equilibrium phase behavior of four- and five-component systems. When predictions are difficult, an attractive alternative is the Edisonian approach to the problem. The historical Edisonian approach has the drawbacks of being laborious and time intensive. To improve the efficiency of the Edisonian approach, combinatorial applications have been developed. Combinatorial methods have been used extensively in biorganic systems, but to date have been applied to only a few inorganic materials applications. Some of these include: alloy superconductors (Hanack, J. J. J. Mat. Sci., 1970, 5, 964); superconducting and magnetoresistive metal oxides (Xiang, X.-D.; Sun, X.; Briceño, G.; Lou, Y.; Wang, K.-A.; Chang, H.; Wallace-Freedman, W. G.; Chen, S. -W.; Schultz, P. G.; Xiang, X-D. Science, 1995, 268, 1738; Briceño, G.; Chang, H.; Sun, X.; Schultz, P. G. Science, 1995, 270, 273); hydrogenation catalysts (Moates, F. C.; Somani, M.; Annamalai, J.; Richardson, J. T.; Luss, D.; Willson, R. C. Ind. Eng. Chem. Res., 1996, 35, 4801); phosphors (Danielson, E.; Devenney, M.; Gianquinta, D. M.; Golden, J. H.; Haushalter, R. C.; McFarland, E. W.; Poojary, D. M.; Reaves, C. M.; Weinberg, W. H.; Wu, X. D. Science, 1998, 279, 837); and nanoparticle substrates for surface enhanced Raman spectroscopy (Baker, B. E.; Kline, N. J.; Treado, P. J.; Natan, M. J. J. Am. Chem. Soc., 1996, 118, 8721).
While many binary, a few ternary electrocatalysts (see Ley, K. L.; Liu, R. C.; Pu, C.; Fan, Q.; Leyarovski, N.; Segré, C.; Smotkin, E. S. J. Electrochem.Soc., 1997, 144, 1543) and a few electrocatalysts (see Danielson, E.; Devenney, M.; Gianquinta, D. M.; Golden, J. H.; Haushalter, R. C.; McFarland, E. W.; Poojary, D. M.; Reaves, C. M.; Weinberg, W. H.; Wu, X. D. Science, 1998, 279, 837) have been investigated for fuel cells, it is anticipated that the combinatorial apparatus of the present invention would result in the discovery of new electrocatalysts.
In a serial evaluation program, the effectiveness of an electrocatalyst is determined by measuring the current density as a function of potential. For combinatorial screening, the traditional method becomes increasingly unwieldy as the number of components increases. The traditional technique also suffers from the fact that most of the phase space from which data is collected is not interesting for electrocatalysis. An indirect, optical screening method was therefore developed that allows simultaneous testing of hundreds of different compositions and pinpointing of the best catalysts, see WO 00/04362. The oxidation of hydrogen generates protons at the electrode surface. In an unbuffered solution, the local pH in the diffusion layer drops considerably with the generation of protons, even at relatively low current density. When the potential of the array is swept slowly from cathodic to anodic potentials, the best catalysts generate protons first. A fluorescent acid-base indicator can be used to detect the catalysts that most efficiently oxidize methanol by screening for regions that luminesce directly above the electrode. An indicator that may be used for these experiments, N−3-pyridin-2-yl-<4,5,6>-triazolo-<1,5-a>-pyridine (PTP, Ni2+ complex ), fluoresence light blue in its acidic form but does not fluoresce in its basic form, see Mori, H; Sakamoto, K.; Mashito, S.; Matsuoka, Y.; Matsubayashi, M.; Sakai, K. Chem.Pharm. Bull., 1993, 41, 1944.
The present invention provides an improved apparatus for use with, for example, the above-described optical screening method of evaluating electrocatalytic activity of a plurality of solid catalysts. By employing a diffuser, the improved apparatus allows a gaseous reagent to be more evenly distributed across an array of catalysts. Through using a reagent mask, reagent is channeled into contact with the catalysts being evaluated, and through using a catalyst mask, interfering background signal and convection of the solution in contact with the catalysts is minimized. The apparatus of the present invention may be employed in methods beyond those described above.